In my copending and jointly filed patent application Ser. No. 231,878 I describe a system for making handle shopping bags wherein a synthetic-resin tube is fed through a cutting station at a predetermined feed speed. A cutter is engaged through the tube at the station so as to subdivide the tube into a pair of tube halves. This cutter is reciprocated back and forth transversely of the tube in the station at such a rate as to form on the transversely confronting cut edges of the halves interfitting and staggered handle flaps. One of the tube halves may then be detoured through a distance equal to an ood-whole-number multiple of half of the bag width and then is realigned with the other tube half with the flaps in transverse alignment. The tube halves are then simultaneously seamed together.
More particularly according to my earlier invention the cutter is a blade and the cutting station has a cutting drum formed with an endless circumferentially extending and undulating cutting groove in which the blade engages radially inwardly. Another undulating guide group parallel to the cutting groove but axially offset therefrom is engaged by a cam follower connected to the blade so that the blade exactly tracks the cutting groove. The drum is rotated at a peripheral speed which normally varies from the feed speed so that the tube slips on the drum. If the peripheral speed of the drum is identical to the feed speed the bag width will be exactly equal to the circumference of the drum. If the peripheral speed is greater the bag width will be shorter than the circumference of the drum, and if the peripheral speed is slower the bag width will be greater than the circumference of the drum. Thus merely by changing the rotation rate for the drum it is possible to vary the bag width.
Thus with the system according to the instant invention merely changing the relationship between the feed speed of the tube and the peripheral speed of the drum allows the bag width to be varied. This allows a single apparatus to produce bags of different widths. Under the prior-art systems switching from one bag width to another was a complicated procedure entailing replacement of expensive die parts. With the system of my earlier invention it is merely necessary to vary the relationship between speeds by either changing an element in the transmission for the feed rollers or the cutting drum, or by simply adjusting a variable-ratio transmission.
When bags bearing indicia are to be produced it becomes absolutely essential, however, that the indicia lie in the center of the sides of the bag. Any minor lack of synchronization will rapidly become important in a mass-production system. For instance if each bag is a mere hundredth of an inch off the perfect spacing after a standard run of a thousand bags the indicia will be displaced ten full inches so that the bags will normally be completely useless. It is therefore necessary to provide an operator to monitor the machine for a substantial time during a production run in order to insure that the indicia remain centered. Even so an error of as little as one thousandth of an inch will quickly ruin a run of bags.